German Patent No. 32 10 770 discloses a process for producing substantially spherical metallic lightweight particles by a wet-chemical metallization of plastic (synthetic resin) particles.
In the known process, foam particles, such as commercially available foam granules, e.g. of polyurethane, are metallized with, e.g. copper or nickel in an electroless process and the plastic cores are decomposed by a pyrolysis at temperatures of about 400.degree. C.
The wall thickness of the particles can be electrolytically increased up to 0.05 mm.
It has been proposed to form moldings from the metallic lightweight spherical particles by sintering them together.
It has also been proposed to use the known hollow metal spheres to make moldings in which hollow metal spheres are incorporated in a matrix consisting of semisolid or hardening materials. The hollow metal spheres may communicate with each other if the individual spheres are open at their points of contact, or the hollow metal spheres are open at their points of contact, or the hollow metal spheres may be separately disposed in the matrix and may be more or less densely packed therein.